1. Field of the Invention
The present invention in general relates to a rail brake apparatus for a linear motor elevator, and more particularly to an apparatus that reduces the weight and volume of the magnetic core, reduces the impact noise caused by the magnetic cores, and prevents a slipping of the brake lining, so that a precise stop location of the elevator car can be ensured.
2. Description of the Conventional Art
Among conventional elevator systems, the winding type elevator system is well known and widely diffuse in the industry thereof. The winding type elevator has a structure whereby a machinery room is installed on the upper portion of the elevator, while cables are connected to the elevator car on one end and a counter weight on the other. The disadvantages are that the size of the winding apparatus is fairly large and the braking system including the braking device must be placed within the machinery room, requiting much room for installation. Accordingly, manufacturing and installation cost are high.
In an attempt to resolve these problems, a linear motor elevator that does not requires a separate machinery room attracts attention.
The linear motor elevator does not require a speed reducer since the linear motor directly drives the elevator system, so that a separate machinery room for installing a winding machine is not needed thereby reducing space thereof and the number of the elevator machine parts installed therein.
With reference to the accompanied drawings, the conventional linear motor elevator will now be explained.
As shown in FIG. 1, a stator 2 is disposed between an upper and lower supporting devices 3 and 4. A rotor 6 slidably receiving the stator 2 thereinto is disposed at a counter weight frame 5.
At both sides of the counter weight frame 5 is disposed a weight guide roller 7 being in contact with a counter weight guide rail 8 (hereinafter referred to `guide rail 8`).
The counter weight frame 5 is suspended by the cable 9 connected to the car 11 through a plurality of pulleys 10 and 10'.
On both sides of the car 11 is disposed a car guide roller 12 being in contact with the car guide rail 13.
On both upper and lower portions of the rotor 6 are disposed an air gap adjusting apparatus 14 being in contact with the stator 2 by a predetermined gap and a rotor noise preventing apparatus(not shown).
On the outer portion of the rotor 6 is disposed a cooling device 15. Between the stator 2 and the rotor 6 is disposed an air gap detecting device 16.
In addition, below the counter weight frame 5 is disposed a rail braking device 17. At the upper pulley 10 is disposed a magnetic drum brake 18.
As described above, the conventional linear motor elevator obtains the driving force from a linear motor consisting of the rotor 6 and stator 2 of which the rotor 6 linearly moves along the stator 2 by an inductive magnetic force generated therebetween when electric power is applied to the rotor 6. By the movement of the rotor 6, the car 11 connected to the counter weight frame 5 by the cable 9 linearly moves in an opposite direction of the movement of the counter weight frame 5.
The conventional linear motor elevator is designed to brake the car 11 by friction force generated between the rail brake device 17 and the guide rail 8, using an electromagnet for generating a braking force of the rail brake device 17.
The conventional rail brake device 17 will now be explained.
First, the basic structure of the electromagnet system with reference to FIG. 2 includes an upper magnetic core 21 with a coil 22 disposed therein and a lower magnetic core 23. Here, both magnetic cores 21 and 23 face each other. When electric power is applied to the coil 22, both magnetic cores 21 and 23 approach each other due to the magnetic force generated therebetween. A spring 24 disposed between both magnetic cores 21 and 23 maintain a distance therebetween. Here, when both magnetic cores 21 and 23 approach together or separated from each other, both magnetic cores 21 and 23 move linearly along a guiding shaft (not shown).
As previously described about the structure of the electric magnetic cores 21 and 23, since the coil 22 is disposed around the upper magnetic core 21, it is larger and heavier than the lower magnetic core 23.
In addition, with reference to FIGS. 2 and 3 showing views of a conventional rail brake apparatus using the electromagnetic core, each end of the brake arms 25 and 26 are connected to the upper magnetic core 21 and the lower magnetic core, respectively. At each end of both brake arms 25 and 26 are disposed linings 27 and 28. At an intermediate portion of the brake arms 25 and 26, there is disposed a shaft 29 for connecting both brake arms 25 and 25, thereby both brake arms 25 and 26 pivot at the center of the shaft 29.
Accordingly, the distance between the linings 27 and 28 becomes narrowed as distance between the upper magnetic core 21 and the lower magnetic core 23 become widened, so that the linings 27 and 28 which are disposed near both sides of the guide rail 8 squeeze the guide rail 8 and thus braking the car 11 and stopping it at a desired location. On the contrary, when the distance between the upper magnetic core 21 and the lower magnetic core is narrowed, the distance between the linings 27 and 28 become widened, thus releasing the guide rail 8, so that the car 11 become operational.
Thus, in an operation of the elevator, the magnetic force between the upper magnetic core 21 and the lower magnetic core 23 is generated when electric power is applied to the coil 22. The distance between the upper magnetic core 21 and the lower magnetic core 23 is narrowed, so that the brake arms 25 and 26 pivot at the center of the shaft 29 and thus the distance between the linings 27 and 28 is widened for freeing the guide rail 8.
FIGS. 4 and 5 show a detailed rail brake apparatus shown previously in FIG. 3. It includes a supporting shaft 30 slidably inserted into the upper magnetic core 21 and the lower magnetic core 23, one end of which is connected with one end of the upper brake arm 25 by a shaft pin 31. One end of the lower brake arm 26 is connected to a bracket 32 by a shaft pin 33. The lower magnetic core 23 with the coil 22 is connected to the bracket 32. At the outer surface of the supporting shaft 30 is disposed a spring 24.
In the drawings, the same reference numerals are given in case of the same number shown in FIG. 3. A reference numeral 34 denotes a washer, 35 denotes a power input cable, 36 denotes an output cable, respectively.
As described above, when electric power is applied to the coil 22 for the operation of the elevator, the distance between the upper magnetic core 21 and the lower magnetic core 23 becomes narrowed, compressing the spring 24 inserted onto the supporting shaft 30 and then the brake arms 25 and 26 pivot at the center of the shaft 29, so that the distance between the linings 27 and 28 become widened and then the linings 27 and 28 enable the guide rail 8 to be free. On the contrary, when current is not applied to the coil 22, the distance between the upper magnetic core 21 and the lower magnetic core 23 is widened by the recovering force of the spring 24 inserted onto the supporting shaft 30. As a result, the distance between the linings 27 and 28 becomes narrowed, so that a braking force is applied to the guide rail 8 and thus stopping the elevator.
However, there are difficulties in designing a linear motor elevator directly using an electromagnet as shown in FIG. 2 because the upper magnetic core 21 is heavier than the lower magnetic core 23. This results in a gap difference between the linings 27 and 28 and the rail during braking, which requires appropriate designing.
If the linings 27 and 28 are placed so that their distances to rail 8 are equal, only one lining, namely lining 28 of the lighter lower magnetic core 23 will contact the guide rail during braking. Thus, the distance from the linings 27 and 28 to guide rail 8 must be made differently to insure proper braking operation.
Accordingly, difficult as it may be, even if a design for the guide rail 8 and the linings 27 and 28 with the appropriate distances for proper braking was made possible, interference due to friction between the lining and the rail that has the narrower distance, during normal elevator operation will be a problem.
Therefore, as shown in FIG. 3, in order to employ the conventional magnetic cores for linear motor elevators, the weight of the lighter lower magnetic core must be increased to match that of the heavier upper magnetic core. But, an increase in production expenses, added weight and more need for space all decrease the efficiency of the elevator system.
With reference to FIGS. 4 and 5, the problems are now explained in more detail. The required size and weight of the upper magnetic core 23 is determined according to the number of the winding of the coil 22 for generating a predetermined magnetic force and then the size and weight of the lower magnetic core 21 is determined thereafter.
The distance between the upper and lower magnetic cores 21 and 23 becomes narrowed by the attraction of the magnetic force therebetween when a current is applied to the coil 22 and when a current is not applied to the coil 22 the distance therebetween becomes widened by the recovering force of the spring 24. At this time, if the weight of the upper and lower magnetic cores 21 and 23 are different from each other, the lower magnetic core 23 which has less weight than the upper magnetic core 21 will have more rotating movement force. When current is cut off and the two magnetic cores repel each other, one-sided friction occurs at the lining 27 due to not having the same gap to the center of the guide rail 8. To insure the same gap distance, the upper magnetic core 21 should have a weight equal to that of the lower magnetic core 23 and the coil 22.
However, if the design satisfying the requirements is achieved, the upper magnetic core 21 with no coil 22 should have enough volume compared with the volume needed for the magnetic force density determined at the lower magnetic core 23 with the coil 22, so that the weight of the rail brake apparatus 17 increase while the workability and costs are worsened.
In addition, as shown in FIG. 5, when the upper magnetic core 21 and the lower magnetic core 23 attract each other due to magnetic force that occurs when current is applied to the coil 22, an impact takes place at the inner surface of each of the upper magnetic core 21 and the lower magnetic core 23, making a noise audible during elevator operation.
In addition, when current is applied to the coil 22, the upper magnetic core 21 and the lower magnetic core 23 are separated from each other, a slip between the guide rail 8 and each of the linings 27 and 28 may happen when braking the elevator according to the delayed separation even though the upper magnetic core 21 and the lower magnetic core 23 should be quickly separated from each other. The slip therebetween can be a cause of elevator malfunction.